Method for preparing thermally cleavable surfactants without deprotonation

ABSTRACT

The present invention describes surfactants of formula (I), 
                         
wherein R, R N , and m are defined herein, processes for their preparation, and methods for their decomposition.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of prior U.S. patentapplication Ser. No. 10/866,475 originally filed Jun. 10, 2004 now U.S.Pat. No. 7,022,861 entitled “THERMALLY CLEAVABLE SURFACTANTS”, which isherein incorporated by reference in its entirety.

STATEMENT OF GOVERNMENT SUPPORT

The United States Government has a paid-up license in this invention andthe right in limited circumstances to require the patent owner tolicense others on reasonable terms as provided for by the terms ofcontract No. DE-AC04-94AL85000 awarded by the U.S. Department of Energyto Sandia Corporation.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to thermally labile surfactants preparedby Diels-Alder (hereinafter “DA”) reactions. In particular, theinvention relates to the sodium sulfonate thermally cleavable surfactantand processes for their preparation.

2. Description of the Related Art

Over the past decade, the development of cleavable surfactants has beena growing field in surfactant science. As the name implies, cleavablesurfactants are molecules that undergo a chemical or physical change ofthe parent molecular structure resulting in a change and/or loss ofsurface-active behavior. Hence, the production of commercially availablecleavable surfactants may find utility in industrial practices wherefoaming or persistent surface-active properties must be diminished aftertheir initial use in “green” chemistry where degradability is of primaryconcern, and in biomedical drug delivery where surfactants could beremoved through biological mechanisms.

To overcome these shortcomings, we describe here the synthesis andcharacterization of two new surfactant compositions which incorporate athermally cleavable DA adduct as the chemical weak-link within thesurfactant molecular structure. In particular, we have utilized thereversible DA reaction between functionalized furans and maleimides asthe basis for thermally cleavable materials. We have previously reportedthe integration of furan-maleimide DA adducts into molecules to producethermally responsive encapsulating polymers, foams, and adhesives aswell as dendrons and dendrimers which reversibly self-assemble (see U.S.patent Ser. Nos. 6,271,335; 6,337,384; and 6,403,753; U.S. PublishedApplication Serial No. 20030116272; and Aubert, J. H., Journal ofAdhesion, 2003, v. 79, pp. 609-616; McElhanon, J. R., et al., Journal ofApplied Polymer Science, 2002, v. 85, p. 1496; and McElhanon, J. R., etal., Organic Letters, 2001, v. 3(17), p. 2681). Also, similar thermallyreversible DA adducts have been reported incorporated into otherresponsive polymers (see Chen, X., et al., Macromolecules, 2003, v. 36,p 1802-1807; and Chen, X., et al., Science, 2002, v. 295, p 1698-1702).

We have previously reported on (McElhanon, J. R., et al., Langmuir,2005, v. 21, pp. 3259-3266) the synthesis and characterization ofsurfactants that possess a furan-maleimide DA thermally activatedweak-link. These surfactants possessed either carboxylate or phenolatepolar head groups and a 12 carbon linear alkyl chain that served as thehydrophobic tail section. These surfactants all require deprotonation ofthe head group through addition of an excess of potassium hydroxide toachieve solubility in water. We present here the synthesis andcharacterization of two sulfonate-based sodium salt DA surfactants thatrequire no deprotonation step or addition of hydroxide and are solublein water and/or polar organic solvents. The surfactants degrade intohydrophilic and hydrophobic fragments after exposure to elevatedtemperatures (>50° C.) and lose all surface-active behavior.

SUMMARY OF THE EMBODIMENTS

In a broad aspect, the invention describes compounds of formula (I),

whereinR_(N) is —L—G, wherein,

-   -   L is -aryl-, -heteroaryl-, —(C₈-C₃₀)alkyl-, —(C₆-C₂₀)haloalkyl-,        —(C₃-C₁₀)cycloalkyl-, or -heterocyclyl-; and    -   G is —S(O)₂OM,        -   wherein M is H, Li, Na, K, Rb, or Cs;            R is —L₁—R′, wherein,    -   L₁ is a bond, —(C₁-C₄)alkyl-O—, -aryl-, or —(C₃-C₁₀)cycloalkyl-;        and    -   R′ is —(C₈-C₃₀)alkyl, —(C₆-C₂₀)haloalkyl, or        —((C₁-C₄)alkyl-O)_(j)—R″, wherein        -   j is an integer from 2 to 100; and        -   R″ is —H or methyl; and    -   m is an integer from 1 to 4.

The invention further describes a process for the preparation ofcompounds of formula (I).

In a further aspect, the invention describes a method for thedecomposition of surfactants according to formula (I), comprisingheating the surfactant above about 55° C. in an optional polar organicsolvent.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the general scheme for synthesis of sulfonate DAsurfactants 3 and 5.

FIG. 2 graphically illustrates the critical micelle concentration (cmc)determination of the furan-maleimide dodecyl sulfonate sodium saltsurfactant 3.

FIG. 3 graphically illustrates the rate of dissociation dependence ontemperature for sulfonate DA surfactant 3.

FIG. 4A graphically illustrates the rate of dissociation for 10 mMaqueous solutions of sulfonate DA surfactants 3.

FIG. 4B illustrates an expanded view of FIG. 4A up to 10 hours.

DETAILED DESCRIPTION OF THE INVENTION

In another aspect, the invention describes the compound according toformula (I), wherein:

-   -   R_(N) is —L—G, wherein        -   L is -aryl-, —(C₈-C₃₀)alkyl-, or —(C₆-C₂₀)haloalkyl-; and        -   G is —S(O)₂OM,            -   wherein M is H, Li, Na, K, Rb, or Cs; and    -   R and m are as defined in formula (I).

In another aspect, the invention describes the compound according toformula (I), wherein:

-   -   R is —L₁—R′, wherein,        -   L₁ is a bond or —(C₁-C₄)alkyl-O—; and        -   R′ is —(C₈-C₃₀)alkyl or —(C₆-C₂₀)haloalkyl; and    -   R_(N) and m are as defined in formula (I).

In a preferred aspect, the invention describes the compound of formula(II),

wherein G, R, and m are as defined in formula (I).

In another aspect, the invention describes the compound of formula (II),wherein

-   -   m is 1 or 2; and    -   G and R are as defined in formula (I).

In a more preferred aspect, the invention describes the compoundaccording to of formula (III),

wherein G and R are as defined in formula (I).

In another aspect, the present invention describes the compound offormula (III), wherein:

-   -   R is —L₁—R′, wherein,        -   L₁ is a bond; and        -   R′ is —(C₈-C₃₀)alkyl or —(C₆-C₂₀)haloalkyl; and    -   G is as defined in formula (I).

In another aspect, the present invention describes the compound offormula (III), wherein:

-   -   R is —L₁—R′, wherein,        -   L₁ is a bond; and        -   R′ is —(C₈-C₃₀)alkyl; and    -   G is as defined in formula (I).

In another aspect, the present invention describes a process to preparea compound of formula (I), comprising the steps of:

-   -   (i) contacting a furanyl compound of formula (IV),

-   -   wherein:    -   R is —L₁—R′, wherein,        -   L₁ is a bond, —(C₁-C₄)alkyl-O—, -aryl-, or            —(C₃-C₁₀)cycloalkyl-; and    -   R′ is —(C₈-C₃₀)alkyl, —(C₆-C₂₀)haloalkyl, or        —((C₁-C₄)alkyl-O)_(j)—R″, wherein:        -   j is an integer from 2 to 100; and        -   R″ is —H or methyl; and    -   m is an integer from 1 to 4;        with a maleimide compound of formula (V),

wherein

-   -   R_(N) is —L—G, wherein:        -   L is -aryl-, -heteroaryl-, —(C₈-C₃₀)alkyl-,            —(C₆-C₂₀)haloalkyl-, —(C₃-C₁₀)cycloalkyl-, or            -heterocyclyl-; and        -   G is —S(O)₂OM,            -   wherein M is H, Li, Na, K, Rb, or Cs; in an optional                polar organic solvent; and    -   (ii) heating the composition to a temperature of about 25° C. to        about 55° C.

In another aspect, the invention describes the process to prepare acompound of formula (I), comprising the steps of

-   -   (i) contacting a furanyl compound of formula (IV),    -   wherein:        -   R_(N) is —L—G, wherein            -   L is -aryl-, —(C₈-C₃₀)alkyl-, or —(C₆-C₂₀)haloalkyl-;                and            -   G is —S(O)₂OM,                -   wherein M is H, Li, Na, K, Rb, or Cs;                    with a maleimide compound of formula (V), in an                    optional polar organic solvent; and    -   (ii) heating the composition to a temperature of about 25° C. to        about 55° C.

In another aspect, the invention describes the process to prepare acompound of formula (I), comprising the steps of:

-   -   (i) contacting a furanyl compound of formula (IV), with a        maleimide compound of formula (V), wherein        -   R is —L₁—R′, wherein,            -   L₁ is a bond or —(C₁-C₄)alkyl-O—; and            -   R′ is —(C₈-C₃₀)alkyl or —(C₆-C₂₀)haloalkyl;                -   in an optional polar organic solvent; and    -   (ii) heating the composition to a temperature of about 25° C. to        about 55° C.

In another aspect, the invention describes the process to prepare acompound of formula (I), comprising the steps of

-   -   (i) contacting a furanyl compound of formula (IV), with a        maleimide compound of formula (VI),

-   -   wherein G is —S(O)₂OM,        -   wherein M is H, Li, Na, K, Rb, or Cs;    -   in an optional polar organic solvent; and    -   (ii) heating the composition to a temperature of about 25° C. to        about 55° C.

In a preferred aspect, the invention describes the process to prepare acompound of formula (I), comprising the steps of

-   -   (i) contacting a furanyl compound of formula (IV), with a        maleimide compound which is N-(4-sodium sulfophenyl) maleimide,        in an optional polar organic solvent; and        -   (ii) heating the composition to a temperature of about            25° C. to about 55° C.

In another aspect, the invention describes the process to prepare acompound of formula (I), comprising the steps of

-   -   (i) contacting a furanyl compound of formula (IV), wherein m is        1 or 2; with a maleimide compound of formula (V), in an optional        polar organic solvent; and    -   (ii) heating the composition to a temperature of about 25° C. to        about 55° C.

In another aspect, the invention describes the process to prepare acompound of formula (I), comprising the steps of

-   -   (i) contacting a furanyl compound of formula (VII),

with the maleimide compound as defined in formula (V), in an optionalpolar organic solvent; and

-   -   (ii) heating the composition to a temperature of about 25° C. to        about 55° C.

In another aspect, the invention describes the process to prepare acompound of formula (I), comprising the steps of

-   -   (i) contacting a furanyl compound of formula (VII),        -   wherein:            -   R is —L₁—R′, wherein,                -   L₁ is a bond or —(C₁-C₄)alkyl-O—; and            -   R′ is —(C₈-C₃₀) alkyl or —(C₆-C₂₀) haloalkyl;                -   with the maleimide as defined in formula        -   (V), in an optional polar organic solvent; and    -   (ii) heating the composition to a temperature of about 25° C. to        about 55° C.

In a preferred aspect, the invention describes the process to prepare acompound of formula (I), comprising the steps of

-   -   (i) contacting a furanyl compound which is 2-docecylfuran or        2-octadecyfuran, with the maleimide compound as defined in        formula (V), in an optional polar organic solvent; and    -   (ii) heating the composition to a temperature of about 25° C. to        about 55° C.

In a more preferred aspect, the invention describes the process toprepare a compound of formula (I), comprising the steps of

-   -   (i) contacting a furanyl compound which is 2-docecylfuran or        2-octadecyfuran, with the maleimide compound which is        N-(4-sodium sulfophenyl) maleimide, in an optional polar organic        solvent; and    -   (ii) heating the composition to a temperature of about 25° C. to        about 55° C.

In a preferred aspect, the present invention describes the process toprepare a compound of formula (I), comprising the steps of

-   -   (i) contacting a furanyl compound of formula (IV) with a        maleimide compound of formula (V), in an optional polar organic        solvent which is N,N-dimethylformamide, and    -   (ii) heating the composition to a temperature of about 25° C. to        about 55° C.

In another aspect, the present invention describes the process toprepare a compound of formula (I), comprising the steps of

-   -   (i) contacting a furanyl compound of formula (IV) with a        maleimide compound of formula (V), in an optional polar organic        solvent which is water, methanol, ethanol, i-propanol,        t-butanol, glyme, diglyme, tetrahydrofuran, acetonitrile,        dimethylsulfoxide, N,N-dimethylfuran, N,N-dimethylacetamide,        N-methylpyrridinone, or mixtures thereof, and    -   (ii) heating the composition to a temperature of about 25° C. to        about 55° C.

In another aspect, the present invention describes the process toprepare a compound of formula (I), comprising the steps of

-   -   (i) contacting a furanyl compound of formula (IV) with a        maleimide compound of formula (V), in an optional polar organic        solvent, and    -   (ii) heating the composition to a temperature of about 30° C. to        about 55° C.

In another aspect, the present invention describes the process toprepare a compound of formula (I), comprising the steps of

-   -   (i) contacting a furanyl compound of formula (IV) with a        maleimide compound of formula (V), in an optional polar organic        solvent, and    -   (ii) heating the composition to a temperature of about 40° C. to        about 55° C.

In another aspect, the present invention describes the process toprepare a compound of formula (I), comprising the steps of

-   -   (i) contacting a furanyl compound of formula (IV) with a        maleimide compound of formula (V), in an optional polar organic        solvent, and    -   (ii) heating the composition to a temperature of about 45° C. to        about 55° C.

In a preferred aspect, the present invention describes the process toprepare a compound of formula (I), comprising the steps of

-   -   (i) contacting a furanyl compound of formula (IV) with a        maleimide compound of formula (V), in an optional polar organic        solvent, and    -   (ii) heating the composition to a temperature of about 50° C. to        about 55° C.

The present invention also describes a method for decomposingsurfactants according to claim 1, comprising heating the surfactant tofrom about 55° C. to about 120° C. in an optional polar organic solvent.

The present invention also describes a method for decomposingsurfactants according to claim 1, comprising heating the surfactant tofrom about 75° C. to about 120° C. in an optional polar organic solvent.

The present invention also describes a method for decomposingsurfactants according to claim 1, comprising heating the surfactant tofrom about 85° C. to about 120° C. in an optional polar organic solvent.

The present invention also describes a method for decomposingsurfactants according to claim 1, comprising heating the surfactant tofrom about 95° C. to about 120° C. in an optional polar organic solvent.

Preparations

The surfactants of the present embodiment comprise simple ringed adductspecies constructed by the well-known DA reaction between appropriatelyfunctionalized furans and maleimides as the basis for these embodiments(FIG. 1). As mentioned, the process of adduct formation typically occursat moderate temperatures (i.e., about 50° C.), whereas dissociationoccurs at temperatures above about 55° C. Surfactant molecules thatcontain the furan-maleimide DA adducts are, therefore, attractivecandidates as surface active materials for processes that requiresurfactant “deactivation” or removal using a non-invasive thermaltrigger.

The examples of the present invention should not be construed aslimiting the scope of the invention to any particular functionalsubstituent. Surfactants contemplated as falling within the scope andmeaning of the present invention, therefore, may use any of the head andtail groups known to the surfactant science arts that can beincorporated into the precursor molecules forming the basis for the DAcycloaddition reaction. In particular, tail groups comprising long alkylchains, with or without branching, having the general formulaC_(n)H_(2n) where n varies from 6 to about 24 and preferably from 6 toabout 18, are considered as within the scope of the present disclosureas are any of the headgroups comprising a sodium sulfonate group.

An alkylfuran is used as the diene molecule and a maleimideincorporating a sodium sulfophenyl group as the dienophile molecule toproduce the desired DA adduct molecules of the present invention. Inthis way the alkylfuran carries with it the non-polar (hydrophobic)“tail” group for the nascent surfactant molecule while the maleimidecarries the polar (hydrophilic) “head” group of the surfactant moleculeas these two molecules are combined by the DA process. The alkylfuran isprepared as generally described by Piancatelli, et al., (Tetrahedron,1980, v. 36(5), pp. 661-663, herein incorporated by reference) by areaction between furan and an alkyl bromide molecule in a solution ofn-butyl lithium and THF. The functional maleimide is prepared asdescribed by Park, et al., (Journal of Polymer Science Part A: PolymerChemistry, 1992, v. 30(5), pp. 723-729, herein incorporated byreference) by a condensation reaction to provide the sodium sulfophenylmaleimide.

DEFINITIONS

The term “alkyl” as used herein, means a hydrocarbon chain of 1 to 30carbons, wherein the chain is linear or branched at any point therein.Examples of alkyl groups include, but are not limited to, methyl,propyl, i-propyl, t-butyl, 2-ethylhexyl, n-decyl, n-eicosyl, and thelike.

The term “aryl” as used herein, means a cyclic aromatic hydrocarboncontaining 5 to 14 carbons, wherein the group may be monocyclic or fusedbicyclic or tricyclic groups. Examples of aryl groups include, but arenot limited to, phenyl, naphthyl, anthracenyl, and the like.

The term “polar organic solvent” as used herein, means a solvent with adielectric constant greater than 6. Examples of polar organic solventsinclude, but are not limited to, water, dimethylsulfoxide, methylenechloride, tetrahydrofuran, methanol, and the like.

The term “cycloalkyl” as used herein, means a saturated cyclichydrocarbon containing 3 to 10 carbons, wherein the rings may bemonocyclic, fused or bridged bicyclic, and fused or bridge tricyclic.Examples of cycloalkyl groups include, but are not limited to,cyclopropyl, cyclohexyl, bicyclo[2.2.2]octyl, adamantyl, decalinyl, andthe like.

The term “heterocyclyl” as used herein, means a saturated cyclic groupcontaining at least one heteroatom, such as N, O, S, or P, andcontaining 3 to 10 total atoms in the ring system. The ring system maybe monocyclic, fused or bridged bicyclic, or fused or bridged tricyclic.Examples of heterocyclyl groups include, but are not limited totetrahydrofuranyl, pyrrilodinyl, piperidinyl, piperazinyl, aziridinyl,oxiranyl, morpholinyl, thiomorpholinyl, and the like.

The term “heteroaryl” as used herein, means an aromatic cyclic groupcontaining at least one heteroatom, such as N, O, S, or P, andcontaining 5 to 14 total atoms in the ring system. The ring system maybe monocyclic, fused bicyclic, or fused tricyclic. Examples ofheteroaryl groups include, but are not limited to, pyridyl, pyrrolyl,thienyl, furanyl, quinolinyl, indolyl, isoindolyl, isoquinolinyl, andthe like.

The term “haloalkyl” as used herein, means an alkyl group, as definedherein, substituted with one or more halogen groups, as defined herein.Examples of haloalkyl groups include, but are not limited totrifluoromethyl, nonafluorobutyl, 2,2,2-trifluoroethyl,1,1-bis(trifluoromethyl)-2,2,2-trifluoroethyl-, 2-chloroethyl,2,2,2-trichloroethyl, dibromomethyl, 3-bromopropyl, iodomethyl, and thelike.

The term “halogen” as used herein means fluoro, chloro, bromo, or iodo.

EXAMPLES Example 1exo-4-Dodecyl-7-oxabicyclo[2.2.1]hept-5-ene-2,3-dicarboxy-N-(4-sodiumsulfophenyl)imide (Compound 3)

To a solution of N-(4-sodium sulfophenyl)maleimide 1 (6.12 g, 22.2 mM)in DMF (40 mL) was added 2-dodecylfuran 2 (26.3 g, 0.11 M). The reactionwas allowed to stir at 50° C. until ¹H NMR showed consumption ofmaleimide starting material 1. The reaction was then concentrated todryness and the residue washed with petroleum ether until excess2-dodecylfuran 2 was removed to yield surfactant molecule 3 (10.7 g,94%) as a tan solid. Surfactant 3 was isolated as a mixture of 96:4exo/endo isomers.

NMR spectra were measured at 500 MHz ¹H and at 125 MHz ¹³C, in DMSO-d₆.Spectral results are as follows:

¹H NMR (500 MHz, DMSO-d₆) exo δ 7.69 (d, J=8.5 Hz, 2H), 7.15 (d, J=8.5Hz, 2H), 6.57 (dd, J=5.0, 2.0 Hz, 1H), 6.51, (d, J=5.5 Hz, 1H), 5.28(dd, J=5.0, 1.5 Hz, 1H), 3.17 (d, J=6.5 Hz, 1H), 2.94 (d, J=6.5 Hz, 1H),2.04-1.98 (m, 1H), 1.84-1.78 (m, 1H), 1.57-1.53 (m, 1H), 1.45-1.39 (m,1H), 1.32-1.13 (m, 18H), 0.84 (t, J=7.0 Hz, 3H).

¹³C NMR (125 MHz, DMSO-d₆) exo δ 175.54, 174.10, 148.13, 138.79, 137.00,132.04, 126.16, 126.15, 91.44, 80.22, 50.47, 49.06, 31.27, 29.43, 29.03,29.00, 28.98, 28.94, 28.92, 28.68, 24.73, 22.07, 13.93.

Example 2exo-4-Octadecyl-7-oxabicyclo[2.2.1]hept-5-ene-2,3-dicarboxy-N-(4-sodiumsulfophenyl)imide (Compound 5)

To a solution of N-(4-sodium sulfophenyl)maleimide 1 (2.02 g, 7.34 mM)in DMF (20 mL) was added 2-octyldecylfuran 4 (11.7 g, 37.9 mM). Thereaction was allowed to stir at 50° C. until ¹H NMR showed consumptionof maleimide starting material 1. The reaction was then concentrated todryness and the residue washed with petroleum ether until excess2-octyldecylfuran 4 was removed to yield surfactant molecule 5 (4.21 g,96%) as a brown solid.

NMR spectra were measured at 500 MHz ¹H and at 125 MHz ¹³C, in DMSO-d₆.Spectral results are as follows:

¹H NMR (500 MHz, DMSO-d₆) exo δ 7.68 (d, J=8.5 Hz, 2H), 7.15 (d, J=8.5Hz, 2H), 6.58 (dd, J=5.0, 1.5 Hz, 1H), 6.51, (d, J=6.0 Hz, 1H), 5.13(dd, J=5.0, 1.5 Hz, 1H), 3.17 (d, J=6.5 Hz, 1H), 2.94 (d, J=6.5 Hz, 1H),2.04-1.98 (m, 1H), 1.84-1.78 (m, 1H), 1.56-1.14 (m, 30H), 0.84 (t, J=6.5Hz, 3H).

¹³C NMR (125 MHz, DMSO-d₆) exo δ 175.52, 174.07, 148.30, 138.78, 136.99,131.94, 126.12, 126.04, 91.42, 80.19, 50.45, 49.05, 31.25, 29.42, 28.99,28.98, 28.96, 28.92, 28.66, 24.73, 22.06, 13.92.

Example 3 Characterization of Aqueous Surfactant Solutions

The surfactants were characterized in terms of their critical micelleconcentration (hereinafter “cmc”). This was achieved through dynamicsurface tension measurements and dye solubilization.

Example 3a Determination of Critical Micelle Concentration by DynamicSurface Tension

The dynamic surface tension measurements were conducted using aSENSADYNE® QC3000 dynamic surface tensiometer (available from theSENSADYNE® Instruments Division of the Chem-Dyne Research Corporation,Mesa, Ariz.) that utilizes the maximum bubble pressure method. Thefundamental operating principles and theoretical considerations of thismethod are explained in detail elsewhere, and a brief summary only isgiven here. Two glass probes with different orifice diameters (0.5 and4.0 mm) were submerged in an aqueous surfactant solution and nitrogenwas bubbled through the samples. Dry nitrogen was used as the bubblesource gas and was delivered to the instrument at 50 psi. The instrumentwas operated at a bubble frequency of 0.5 Hz to approximate equilibriumsurface tension values for each sample. The differential pressure signalgenerated by bubble formation is related to the interfacial surfacetension of the liquid and gas. Surface tension calibration was carriedout by measuring the surface tension of deionized water and ethanol andcomparing to known literature values. Solution temperature was monitoredwith a calibrated thermistor (±0.1° C.) attached to the orifice probes.Instrumental calibration was conducted for every change in experimentalconditions and after prolonged periods of instrumental quiescence. Allexperiments were conducted at 25.0±0.2° C. unless otherwise noted. Timeaveraging of the data produced values that differed by less than 0.2mN/m from the mean.

Example 3b Determination of Critical Micelle Concentration by DyeSolubility

To determine the enhanced solubility of a water-insoluble dye (OrangeOT) in the presence of the oily cores of micelles that exist above thecritical micelle concentration, an excess amount (0.02 g per 10 mL ofaqueous sample) of the dye was added to a series of aqueous surfactantsolutions and ultrasonically agitated using a SONICATOR® for 30 minutesin a water bath operated under ambient conditions. The solutions werethen removed from the SONICATOR® and allowed to settle under ambientconditions for 2 hours. The solutions were filtered using 0.2 μmpolyvinylidene fluoride (PVDF) syringe filters (obtained from WhatmanInc., Florham Park, N.J.) into 3.5 mL 1 cm path length quartz cuvettes(available from Starna Cells, Inc., Atascadero, Calif.). The amount ofdye solubilized in each sample was measured by monitoring the absorbancewavelength of each with a Shimadzu 2401-PC UV-Vis Dual BeamSpectrophotometer (obtained from Shimadzu Scientific Instruments (SSI),Pleasanton, Calif.) operating at ambient conditions with surfactantsolutions without dyes serving as the sample background.

Example 4 Results of CMC Determinations

The results obtained from surface tension measurements as a function ofconcentration for surfactant 3 are presented in FIG. 2. The data followsthe classic surface-active profile plot, with two distinct inflectionpoints followed by plateau regions. The first inflection point,occurring at very low concentrations, indicates the initial surfactantadsorption at the gas-liquid interface that lowers the effective surfacetension of the liquid. The relationship between concentration andsurface tension is relatively monotonic at concentrations greater thanthis lower inflection point. The second inflection point, which occursnear 5 mM, is the result of the formation of a fully saturatedgas-liquid interface by the surfactant, and it is at this point thatmicelles begin to form. The surface tension values above thisconcentration are observed to remain relatively constant.

The results from determination of cmc for surfactant 3 using dyesolubility are also presented in FIG. 2. It can be seen that at lowconcentrations (<1 mM), very little dye is present in the aqueoussamples, which is in agreement with the published solubility data forthe dye. Once the concentration is increased above 1 mM, however, thereis a marked increase in the observed dye absorbance at 523 nm (theanticipated peak absorbance wavelength). This indicates that more of theoil-soluble dye is present in solution. The increase in the apparentsolubility of the dye is explained by the presence of micelles thatpossess “oily” cores that are favorable to the dye. As the concentrationis increased, the amount of dye is also observed to increase in amonotonic fashion. This is due to an increase in the number of micellespresent in solution as the concentration is increased beyond the cmc.

The cmc of the dodecyl sulfonate sodium salt surfactant is thereforedetermined to be 1.3 mM through dye solubilization and 5.1 mM by dynamicsurface tension measurements. This apparent discrepancy is explained bythe fact that one (dye solubilization) is a static probe of the micellarenvironment, whereas the other (dynamic surface tension) is a dynamicprobe of the gas-liquid interface. The dynamic probe will always producehigher apparent values of the cmc as it is creating a new gas-liquidinterface and thus decreases the amount of bulk surfactant in solutionover time.

Example 5 Demonstration of Retro-DA Degradation Via Surface Tension

The surfactants of the invention undergo the retro-DA reaction afterexposure to elevated temperatures. To determine the effect oftemperature on surface tension as a measurement of surfactantdegradation, 10 mM (2×cmc as determined by surface tensiometry)solutions of the surfactants in water were prepared. Data were recordedfor is all experiments via a computer interface using the SENSADYNE®QC3000 version 5.3 software. The data obtained from these experiments ispresented in FIG. 3 and indicates that the surfactants possess differentrates of degradation based on the temperatures to which they areexposed.

Additional measurements to determine the effect of temperature on therates of surfactant dissociation and loss of surface active propertieswere conducted on 10 mM solutions of surfactant 3. The data shown inFIG. 3 clearly indicate that the temperature at which the samples areelevated to has a dramatic impact on the rate at which the surfaceactive properties are lost in these solutions. At the highesttemperature, 95° C., there is a loss of all surface activity and thesurface tension is that of water within 1 hour of exposure. At thelowest temperature monitored, 55° C., it takes over 30 hours of exposureto eliminate surface activity. The data has been fit with a logistic4-parameter algorithm using SIGMAPLOT® (available from Systat Software,Inc., Richmond, Calif.). The resultant fits to the data are reasonableand are within 5% error and achieved R² values greater than 99.0%. Thisdata provides the baseline for “tailoring” the surface activity of asystem based on at least three parameters: (a) initial surfactantconcentration utilized, (b) temperature, and (c) time at temperature.The effective control of the surface active properties of the system isenvisioned to be accomplished by manipulating one or any combination ofthese parameters. It should also be noted that all of the surfacetension measurements of the cleaved samples were taken after the sampleshad cooled to ambient conditions, and are convincing evidence that thedissociation accompanying the retro DA is irreversible in micelles.

Example 6 Demonstration of Retro-DA Degradation Via NMR

Detailed solution-based thermal degradation experiments on surfactant 3were also monitored by ¹H NMR to elucidate degradation rates at avariety of temperatures. The data for 10 mM aqueous samples ofsurfactant 3 heated isothermally over time are shown in FIGS. 4A and 4B.Percent degradation was tracked by recording the decrease in theintegral value for the bridge head proton of the DA adduct located at5.02 ppm. At the highest temperature tested, 95° C., surfactant 5 wascompletely degraded after about 1 hour of heating. At 65° C., surfactant3 completely degraded after about 10 hours of heating. It is importantto note that the percent degradation of surfactant 5 over varioustemperatures is not necessarily linear. This is a result of the K_(eq)for the reversible DA reaction with DA adduct formation/stabilitydominating at lower temperatures.

Finally, to the extent necessary to understand or complete thedisclosure of the present invention, all publications, patents, andpatent applications mentioned herein are expressly incorporated byreference therein to the same extent as though each were individually soincorporated.

Having thus described exemplary embodiments of the present invention, itshould be noted by those skilled in the art that the disclosures hereinare exemplary only and that various other alternatives, adaptations, andmodifications may be made within the scope of the present invention.Accordingly, the present invention is not limited to the specificembodiments as illustrated herein, but is only limited by the followingclaims.

1. A process to prepare a compound according to formula (I),

wherein R_(N) is —L—G, wherein L is -aryl-, -heteroaryl-,—(C₈-C₃₀)alkyl-, —(C₆-C₂₀)haloalkyl-, —(C₃-C₁₀)cycloalkyl-, or-heterocyclyl-; and G is —S(O)₂OM, wherein M is H, Li, Na, K, Rb, or Cs;R is —L₁—R′, wherein, L₁ is a bond, —(C₁-C₄)alkyl-O—, -aryl-, or—(C₃-C₁₀)cycloalkyl-; and R′ is —(C₈-C₃₀)alkyl, —(C₆-C₂₀)haloalkyl, or—((C₁-C₄)alkyl-O)_(j)—R″, wherein j is an integer from 2 to 100; and R″is —H or methyl; and m is an integer from 1 to 4, comprising the stepsof: (i) contacting a furanyl compound of formula (IV),

wherein R is —L₁—R′, wherein, L₁ is a bond, —(C₁-C₄)alkyl-O—, -aryl-, or—(C₃-C₁₀) cycloalkyl-; and R′ is —(C₈-C₃₀)alkyl, —(C₆-C₂₀)haloalkyl, or—((C₁-C₄)alkyl-O)_(j)-R″, wherein j is an integer from 2 to 100; and R″is —H or methyl; and m is an integer from 1 to 4; with a maleimidecompound of formula (V),

wherein R_(N) is —L—G, wherein L is -aryl-, -heteroaryl-,—(C₈-C₃₀)alkyl-, —(C₆-C₂₀)haloalkyl-, —(C₃-C₁₀)cycloalkyl-, or-heterocyclyl-; and G is —S(O)₂OM, wherein M is H, Li, Na, K, Rb, or Cs;in an optional polar organic solvent; and (iii) heating the compositionto a temperature of about 25° C. to about 55° C.
 2. The processaccording to claim 1, wherein R_(N) is —L—G, wherein L is -aryl-,—(C₈-C₃₀)alkyl-, or —(C₆-C₂₀)haloalkyl-; and G is —S(O)₂OM, wherein M isH, Li, Na, K, Rb, or Cs.
 3. The process according to claim 1, wherein Ris —L₁—R′, wherein, L₁ is a bond or —(C₁-C₄)alkyl-O—; and R′ is—(C₈-C₃₀)alkyl or —(C₆-C₂₀)haloalkyl.
 4. The process according to claim1, wherein the maleimide compound is of formula (VI),


5. The process according to claim 4, wherein maleimide compound isN-(4-sodium sulfophenyl) maleimide.
 6. The process according to claim 1,wherein m is 1 or
 2. 7. The process according to claim 1, wherein thefuranyl compound is of formula (VII),


8. The process according to claim 1, wherein R is —L₁—R′, wherein, L₁ isa bond or —(C₁-C₄)alkyl-O—; and R′ is —(C₈-C₃₀)alkyl or—(C₆-C₂₀)haloalkyl.
 9. The process according to claim 1, wherein thefuranyl compound is 2-docecylfuran or 2-octadecyfuran.
 10. The processaccording to claim 1, wherein the polar organic solvent is water,methanol, ethanol, i-propanol, t-butanol, glyme, diglyme,tetrahydrofuran, acetonitrile, dimethylsulfoxide, N,N-dimethylfuran,N,N-dimethylacetamide, N-methylpyrridinone, and mixtures thereof. 11.The process according to claim 10, wherein the solvent isN,N-dimethylformamide.
 12. The process according to claim 1, wherein thetemperature is from about 30° C. to about 55° C.
 13. The processaccording to claim 1, wherein the temperature is from about 40° C. toabout 55° C.
 14. The process according to claim 1, wherein thetemperature is from about 45° C. to about 55° C.
 15. The processaccording to claim 1, wherein the temperature is from about 50° C. toabout 55° C.